Stripping zone

A continuous circulation of groundwater is generated in the area surrounding the remediation well, as aquifer waters replace the annulus water. The circulation thus delivers new contaminants to the stripping zone. Volatile contaminants dissolved in the groundwater are transferred from the liquid to the gas phase and are extracted from the groundwater surface via a double-cased screen. Soil air from the unsaturated zone is also extracted and transported to the off-gas treatment system. 

Hydrothermal (steam) stability is also important, in as much as the catalyst must pass through a high temperature stripping zone in which the usual fluid stripping medium is steam. In our laboratory, zeolite hydrothermal stability is measured by comparing the x-ray crystallinity of the unknown faujasite sample with that of a fully rare earth exchanged reference standard following a 3 hour, 100% steam, 1500 F treatment. 

The background of shortcut methods is well treated in the books of King (1980) and Henley and Seader (1981). Here attention will be directed to application of the techniques. These shortcut methods assume constant molal overflow in the rectifying and stripping zones and constant relative volatilities, which may be taken at the conditions of the feed tray or as a geometric mean of the values at the top and bottom of the column. Since the top conditions are not known completely in advance, evaluation of a mean relative volatility is an iterative process that can be started with the value at the feed tray or at the feed condition. Particular modes of variation of a sometimes are assumed. The method of Winn assumes that the vaporization equilibrium ratios vary as... 

In the reactor, the coke particles flow down through the vessel into a stripping zone at the bottom. Steam displaces the product vapors between the particles, and the coke then flows into a riser that leads to the burner. Steam is added to the riser to reduce the solids loading and to induce upward flow. The average bed temperature in the burner is 590-650°C (1095-1200°F), and air is added as needed to maintain the temperature by burning part of the product coke. The pressure in the burner may range from 5 to 25 psi. Flue gases from the burner... 

A usual solution in this case is a sequence of a reactor and several separation units (Figure 5). Another way—an integrated RD process such as shown in Figure 6— allows for simultaneous formation of methyl acetate in the reaction zone, extractive distillation and product enrichment in the upper part of the column, and methanol separation in the stripping zone. The production of esters such as methyl acetate, ethyl acetate, and butyl acetate has for years been an interesting RD application. 

The concentration profiles are displayed in Figure 3.15 (right-hand). The first column has 50 theoretical trays with feed on 20, entrainer/feed ratio 2 and reflux ratio 3.5. A bound in the concentration profile takes place around the feed. In the stripping zone the toluene carries out preferentially the chloroform. The rectification part separates mainly the binary acetone-chloroform, the entrainer concentration being negligible. The profile of the second column... 

The feasibility of the above setup can be evaluated by simulation with Aspen Plus [19]. The RD column is built-up as a reboiled stripper followed by a condenser and a three-phase flash, with organic phase refluxed to column. The result is that only 3 to 5 reactive equilibrium stages are necessary to achieve over 99% conversion. The stripping zone may be limited at 2-3 stages, while the rectification zone has 1-2 stages. 

The simulation shows that acroleine is the most difficult to isolate. If not removed in C-1A it will be found in the top of C-2 and further in the end product The column C-1A is designed with a ratio stripping/rectificahon 3 1 to ensure over 99.9% HCN recovery. Despite a Rvalue of 1.7 the acroleine concentrates in the middle of the stripping zone, from which a quantitative removal by a large side stream or secondary recovery column is not efficient. The best solution is chemical conversion in heavies. 

In the reactor, the coke particles flow down through the vessel into a stripping zone at the bottom. Steam displaces the product vapors between the particles, and the coke then flows into a riser that leads to the... 

Let s consider the separation of a binary minimum azeotrope AB with a medium boiling entrainer C (Fig. 9.12). Note that the AB azeotrope and the component B are nodes, while both A and C are saddles. The separation regions for the first split are delimited by direct and indirect sequences, respectively. If the boiling points of A and AB azeotrope are not too close, A can be obtained as distillate, even if it is a saddle Rooks et al. (1998) has given recently a consistent explanation the split is feasible when the concentration profiles of both rectification and stripping zones points to the same common saddle, in this case the component C. 

The ethanol column (C-1) has practically only stripping zone. Fig. 9.31-left shows composition profile both for liquid and vapour phase. The examination of the composition profiles highlights the role of the entrainer. In the zone close to the top the benzene extracts the ethanol in the liquid phase, and as a result increases the volatility of water, so that on lower stages the water is completely removed. In the lower part practically only the binary ethanol/benzene remains. The distillation trajectory starts from the ternary azeotrope, goes along the ethanol/ benzene saddle and terminates in the ethanol vertex. Because the boiling point of the azeotrope ethanol-water is close to the pure ethanol, the profile could easily jump to the ethanol/water azeotrope. Consequently, the design and operation of the column (C-1) is very sensitive. 

Determine the feed condition q. This signifies the moles of liquid going to the stripping zone from one mole of feed, and can be found as follows ... 

The simplest method is to start with the rectification zone by drawing the corresponding line from the point x = Xp and find the intersection with the g -line. Then the operating line for the stripping zone is simply joining this point with x. ... 

Stripped Matrix. For use in all LRRs except V, W, X, and Y. A layer starting within 15 cm (6 in.) of the soil surface in which iron/manganese oxides or organic matter have been stripped from the matrix, exposing the primary base color of soil materials. The stripped areas and translocated oxides or organic matter form a faint diffnse splotchy pattern of two or more colors. The stripped zones are 10% or more of the volnme they are rounded and approximately 1-3 cm (0.5-1 in.) in diameter (Figure 3.25). 

In rectification processes, continuously operated vaporizers are used as simple continuous distillation devices. The vaporizer, usually a circulating evaporator, forms the first practical separation stage of the stripping zone of the rectification column. 

Thin film distillation and rectification may be combined in such a way that the thin film evaporator is connected to a column with both an enrichment and a stripping zone, or just an enrichment zone [2.17]. Such a combination is particularly useful for separation of sensitive mixtures in a vacuum. 

Continuously Operated Rectification in Rectification Columns with Enriching and Stripping Zones... 

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